Potential for Biological Control of Rice Yellow Mottle Virus Vectors

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POTENTIAL FOR BIOLOGICAL CONTROL OF RICE YELLOW MOTTLE VIRUS VECTORS

N. WOIN, DJONMAÏLA1, SADOU ISMAEL, SALI BOUROU and T. BEBOM IRAD, Box 33 Maroua, Cameroon 1University of Dschang, Box 222 Dschang, Cameroon

ABSTRACT

Insect pests and disease infestations are the primary constraints in rice (Oryza sativa) production systems in Africa and Asia. For Cameroon in particular, the rice yellow mottle virus (RYMV) is increasingly a serious problem to rice production. During the poulations of the various insect vectors of RMYV are not known, and hence the need for this study. Unfortunately, 2002 - 2004, two sampling methods were combined to assess the population of insects vectors of rice yellow mottle virus (RYMV) in the three major irrigated rice ecosystems in northern Cameroon (Lagdo, Maga and Yagoua), and in low land rice fields. Sampling was conducted using sweep net and D-Vac (sucking trap) fortnightly in 2002 and 2003 until mid October in low land rice fields, while in the irrigated fields, samplings occurred between December and April. Rearing using dead insects was conducted simultaneously in the laboratory to identify the parasitoid insect species. From samples obtained at different sites: (i) the dominant structure of the RYMV insect vectors was analysed according to the rice phenology; and (ii) the diversity and the occurrence of potential major groups of predators and parasitoids were assessed. Among the RYMV insect vectors sampled: Chaetocnema pulla Chapuis (Coleoptera: Chrysomelidae), Chnootriba similis Mulsant (Coleoptera: Coccinellidae), Trichispa sericea Guerin-Meneville (Coleoptera: Chrysomelidae), Locris rubra Fabricius (Hemiptera: Cicadellidae), Oxya hyla Stål (Orthoptera: Acrididae), and Conocephalus longipennis (de Haan) (Orthoptera: Tettigoniidae) were the most encountered insect species during the rice growing seasons. With regard to predator populations, spiders (Araneae) were the most abundant, with high concurrency of Pardosa spp (> 42 %) in all sites. In Maga and Yagoua sites, the carabid beetle species, Abacetus crenulatus Dejean and Abacetus foveolatus Chaudoir, were the most numerous whereas the Lagdo site was highly colonised by Clivina. erythropyga Putzeys. Paederus sabaeus Erichson, and Stenus ravus Puthz were the most abundant Staphylinid beetles. From reared dead RYMV insect vectors, Eurytoma spp., Pediobius spp., Tetrastichus spp. and Telenomus spp. emerged as parasitoids. Results of this study reveal a great potential of biological control against rice yellow mottle virus vectors using predators and parastoids. This potential should be developed to manage the yield losses caused by the virus infection in rice cropping systems.

Key Words: Cameroon, Oryza sativa, parasitoids, predators

RÉSUMÉ

Les infestations dues aux insectes et les maladies sont les contraintes primaires dans le système de production du riz (Oryza sativa) en Afrique et en Asie. Pour le Cameroun en particulier, le virus marbre jaune de riz (RYMV) est de plus en plus un problème sérieux à la production de riz. Cependant, les populations des divers vecteurs d’insecte de rmyv ne sont pas connu, et donc le besoin pour cette étude. Malheureusement entre 2002 et 2004, deux méthodes d’échantillonnages ont été combinées pour évaluer la population de vecteurs d’insectes de virus marbre jaune de riz (RYMV) dans les trois écosystèmes majeurs de riz irrigué au nord du Cameroun (Lagdo, Maga et Yagoua), et dans les champs de riz de terre bas. L’essai a été dirigé utilisant le coup de balai net et D- vac (suçant le piège) les nuits de 2002 et 2003 jusqu’ a mi-octobre dans les champs de riz de terre bas, pendant que dans les champs irrigué, les échantillons sont arrivés entre Décembre et Avril. Utilisation des insectes morts était simultanément dirigée dans le laboratoire pour identifier l’espèce d’insecte parasitaire. Des échantillons obtenus aux sites différents: (i) la structure dominante des vecteurs d’insecte de rymv a été analysée selon la phénologie 212 N. WOIN et al. de riz ; et (ii) la diversité et l’événement de groupes majeurs potentiels de prédateurs et de parasitoides ont été évaluées. Les vecteurs d’insecte de RYMV : Chaetocnema pulla Chapuis (Coleoptera : Chrysomelidae), Chnootriba similis Mulsant (Coleoptera : Coccinellidae), Trichispa sericea guerin meneville (Coleoptera : Chrysomelidae), Locris rubra Fabricius (Hemiptera : Cicadellidae), Oxya hyla stål (Orthoptera : Acrididae), et Conocephalus longipennis (de Haan) (Orthoptera : Tettigoniidae) étaient les espèces d’insecte le plus communes pendant les périodes de croissance de riz. En ce qui concerne les populations de prédateur, les araignées (Araneae) étaient le plus abondant, avec haute concurrence de Pardosa spp. (> 42 %) dans tous les sites. Sur les sites de Maga et Yagoua, l’espèce de coléoptère de carabid, abacetus crenulatus dejean et Abacetus foveolatus Chaudoir, étaient les plus nombreux tandis que sur le site de Lagdo a été extrêmement colonisé par Clivina. erythropyga Putzeys. Paederus sabaeus Erichson, et Stenus ravus Puthz étaient les coléoptères du Staphylin le plus abondant. Les vecteurs d’insecte de RYMV, Eurytoma spp., Pediobius spp., Tetrastichus spp., et Telenomus spp. ont émergé comme parasitologies. Les résultats de cette étude révèlent un grand potentiel de contrôle biologique contre les vecteurs de virus marbre jaune de riz utilisant des prédateurs et des parasitoses. Ce potentiel devrait être développer pour gérer les pertes de rendement causées par l’infection de virus dans le système de riz.

Mots Clés: Cameroun, Oryza sativa, parasito¿des, prédateurs

INTRODUCTION Cameroon in year 2 000 (Traoré et al., 2001), studies have never been carried out on RYMV Africa produces only 2.7% of the world’s rice nor on its vectors. (Oryza sativa) and is the second largest rice The aim of this work was to assess the species importing region in the world (6.5 metric in 2003). diversity and population abundance of RYMV Africa’s rice imports represent about 25% of the insect vectors including those of their potential world rice importation (Méndez del Villar, 2003). natural antagonists in lowland/irrigated rice fields With an average yield of 2 t ha-1. With the in the Sudano-sahelian savannah of Cameroon exception of Egypt, rice production in Africa with a view of establishing the potential of remains significantly below the world average and biological control strategies against RYMV regional averages such as Asia (3.8 t ha-1), Latin vectors. America (3.0 t ha-1) and United States (7.0 t ha-1), according to FAO (published online). Compared MATERIAL AND METHODS to the other West African countries, the yearly amount of rice importation in Cameroon is at least Experiments were conducted from 2002 to 2004 in 62 % of thequantity needed. the Sudano-sahelian climate, with a relative Insect pests and diseases are the major humidity of 65 ± 25 %, temperature range of 13- constraints limiting rice production in Africa and 42°C, and mean annual rainfall of 1,000 mm. Three Asia. Of all the rice diseases, the one caused by sites, at least 200 km apart, were sampled. These the rice yellow mottle virus (RYMV), first reported were (1) Lagdo: 9° 3' 0N; 13° 43' 60E - 232 m a.s.l; in Kenya in 1966, is one of the most damaging in Maga: 10° 50' 12N; 14° 56' 37E – 305 m a.s.l, and Africa. The RYMV has by far been reported in Yagoua: 10° 20' 34N; 15° 14' 26E – 313 m a.s.l. The many countries in East and West Africa including experimental fields consisted of a plot (0.5 ha) in Cameroon, where in some cases whole fields each site. Sampling in lowland rice was carried have been devastated. Based on available out only in Lagdo and Yagoua where field plots evidence, RYMV has only been reported from were contiguous to farms cropped by maize (Zea the African continent and is endemic in every mays L.). country where it has been reported. Among the The RYMV vectors and their natural enemies known vectors of the disease insects constitute populating the aerial rice parts were sampled using one of the indubitable and important group. Since 2 methods as described: evidence of the existence of the disease in Biological control of rice yellow mottle virus vectors 213 (i) sweeping with net: 200 doubled sweeps (50 International Institute of Entomology (CAB random sweeps per plot along diagonal and International, London) for identification or median transects); and confirmation. (ii) sucking with D-Vac: 10 sucking of one (1’) at To compare diversity values estimated with 15 m and 100 m from the edge of the plot. the Shannon–Weiner index (H’) on the basis of the frequency distribution of the beetles, Dead RYMV vector materials were reared to parametric statistical techniques were questioned confirm emergence of parasitoids through a t-test (MacArthur, 1965; Poole, 1974) at 5%. All the experimental fields had not been treated with insecticides in the 10 years preceding the RESULTS study. All arthropods sampled were labeled, stored at -4°C, sorted in the laboratory under a Population abundance of RYMV insect vectors. stereoscopic binocular microscope, and then In the 3 locations of the study, the RYMV insect transferred into 70% alcohol, pending vectors sampled were: Chaetocnema pulla identification. Chapuis (Coleoptera: Chrysomelidae), As species diversity combines the area of Chnootriba similis Mulsant (Coleoptera: ‘number of species’ (species richness) and the Coccinellidae) Trichispa sericea Guerin- way in which the individuals are apportioned into Meneville (Coleoptera: Chrysomelidae), Locris those species (evenness) (Vandermeer, 1981), the rubra Fabricius (Hemiptera: Cicadellidae), Oxya heterogeneity of such a community is determined hyla Stål (Orthoptera: Acrididae) and using the Shannon-Weiner index (Risch et al., Conocephalus longipennis (de Haan) 1983). (Orthoptera: Tettigoniidae). The frequency distribution was assessed From 2002 to 2004 (Figs. 1, 2 and 3), C.similis considering dominance class according to was always the most dominant species in Lagdo Engelmann (1978). Representative specimens of rice fields, with an overall frequencies between rove and ground beetles were sent to the 55 and 70% of the total number of vectors caught;

Lagdo 70 Maga

30 Frequency

0 C. pulla C. similis T. sericae L. ruba O. hyla C. longipennis

Figure 1. Frequency distribution of RYMV insect vectors in rice plots at Lagdo and Maga, Cameroon in 2002. 214 N. WOIN et al. Frequency

Figure 2. Frequency distribution of RYMV insect vectors in rice plots at Lagdo, Maga and Yagoua, Cameroon in 2003. Frequency

Figure 3. Frequency distribution of RYMV insect vectors in rice plots at Lagdo, Maga and Yagoua, Cameroon in 2004 Biological control of rice yellow mottle virus vectors 215 followed by O. hyla. In the same period, c) The Staphylinids. The overall trend in C.longipennis occurred most frequently in frequency distribution (cumulative values) of Maga, followed by O. hyla and T.sericea. In rove beetle species is presented in Tables 6 and Yagoua, where sampling was carried out only in 7. When considering the accumulation of irrigated rice fields during 2003 and 2004, the different species encountered, one notices that meadow grasshopper C.longipennis was highly the dominant species are limited to only a few: dominant throughout both cropping seasons, Paederus sabaeus, Stenus ravus and Stenus followed by O. hyla, L.rubra, T. sericea and (Mendicus) S. fulgidus C.pulla. d) Some dominant parasitoids. Among the Populations of predators colonising rice fields potential parasitoids obtained by rearing dead in the sites insect vectors of RYMV, several hemepteran species observed in different localities (Table 8). a) Spiders. Throughout the sampling period 16,968 spider specimens belonging to 28 species DISCUSSION and 10 families were collected from the 3 sites, (Table 1). The species richness was different at Based on existing literature, this study represents Lagdo and Yagoua during 2002. Values the first report of the insect vector species being fluctuated from year to year at Lagdo where present in Cameroon and their role as a vector of populations ranged between 1,862 and 2,394 RYMV. The fact that the prevalence of the species individuals. The abundance was higher in Yagoua investigated differs from one site to another, (2,874 specimens) than in Lagdo (2,394 indicates that pest problems may vary from one individuals), during the same year. However, area to another in view of the diverse and this fact was not concomitant with higher species surrounding conditions under which rice is richness in Lagdo. Shannon index marginally grown. Habitat preference of C. similis appears varied between sites and years (Table 2). to be Lagdo. In Nigeria, Alam (1992) indicated Ten species (82.40 %) were common to all that C. similis occurs in all climatic zones, from sites (Table 3). Lycosidae specimens represented the humid tropical to the Sudanian savanna. 55.08% of the total sample among which Pardosa However, populations of C. similis are lower than spp. accounted for 42.03%, followed by Arctosa that of most other pests reported in Nigeria. spp. (5.60%). In 2 sites, Pardosa spp. were the Akinsola and Agyen-Sampong (1984) reported most dominant species throughout the sampling similar observations for West Africa as a whole. period. Its population abundance in Lagdo Various reports (e.g., Bakker, 1971; Reckhaus and ranged from 38.39 to 51.63% of the total specimens Andriamasintseheno, 1997) observed a positive collected. This was followed by Maga where relationship between vector number and RYMV 44.40% of specimens belonged to Pardosa spp. infection. whereas in Yagoua the species came second Conocephalus longipennis has been reported (20.76%) after Langbiana vokrensis Bosmans as being a transmission agent for RYMV in West and Van Hove (27.35%). Africa (Abo, 1998; Nwilene, 1999). Conocephalus populations were highest in the b) The carabids. The overall trend in cumulative Guinea savanna zone (E.A. Heinrichs and C. frequency distribution (%) of species is presented Williams, WARDA, 1995, unpubl. data). The in Table 4, whereas, Table 5 gives number of status of this pest in the Sudanian savanna has ground beetle species collected for the same not been reported. Studies on the continuum period. Abacetus crenulatus Dejean were the toposequence on the WARDA M’bé Farm dorminant ground beetle species at Lagdo and indicated a trend similar to that of Chaetocnema. Yagoua (Table 4). Overall, Pterostichinae ground Populations occurred in all ecologies but were beetles were the most abundant followed by highest in the uplands (Heinrichs and Barrion, Scaritinae (Table 5). 2004 ). In Latin America, intensification of crop 216 N. WOIN et al. 1,491 Yagoua site Total Yagoua site 1,236 1,031 792 948 1,132 539 593 7,131 Lagdo site Maga site 2002 2003 2004 2002 2003 2004 2003 2004 Roewer 53 73 33 91 79 27 74 382 812 Bosmans 10 11 6 21 20 8 0 199 275 Strand 10 19 32 22 12 21 0 2 118 Simon 26 29 9 22 7 16 0 26 135 (O.P. –Cambridge) (O.P. 6 0 11 13 36 10 0 1 77 (Strand) 61 37 198 109 89 68 0 11 573 (Walckenaer) 149 214 148 158 187 129 34 472 spec. 0 2 19 7 23 2 41 0 94 spp. 29 29 17 31 19 24 44 13 206 spec.spec. 45 17 19 31 11 41 21 31 4 27 29 34 23 6 15 24 167 211 spec. 8 14 3 0 24 31 33 61 174 spec. 43 57 15 21 45 53 9 4 247 spec. 87 73 56 108 68 8 0 23 423 spp. 860 spec. 61 101 126 159 231 174 89 10 951 spp. 63 69 23 44 21 82 63 23 388 rochosa Oxyopes Arctosa Lycosa Pterartoria Notioscopus Phidippus Ostearius melanopygius Metaleptyphantes foulfouldei Oxyopes pallidecoloratus Heliophamus cassinicola Lycosidae Neoscona theisi Allocosa Pardosa

Araneidae TABLE 1. Population density of spiders species collected from 2002 – 2004 on rice in Cameroon TABLE /speciesFamily Araneus cereolellus Clubionidae Cheiracanthium melanostomelum Clubiona Linyphiidae Lepthyphantes spp. 4 0 23 11 43 9 0 78 168

T Oxyopidae Salticidae

Biological control of rice yellow mottle virus vectors 217 1,011 teTotal site Yagoua Lagdo site Maga si 42 50 98 58 12 11 3 18 282 2002 2003 2004 2002 2003 2004 2003 2004 1,862 2,394 2,229 2,063 2,112 2,220 1,214 2,874 16,968 Bosmans & Van Hove Bosmans & Van 11 8 93 5 17 2 94 781 Pickard-Cambridge 58 43 71 108 32 97 13 4 426 Lassert 11 56 11 4 15 21 23 0 141 . spp. 7 15 32 0 4 21 0 6 85 spp spec. 0 9 6 3 0 34 2 8 54 spp. 96 121 49 102 89 77 124 117 775 spec. 37 45 19 93 21 9 0 3 227 spec. 68 33 48 29 39 91 0 0 308 Suffucioides Langbiana vokrensis Theridion Tetragnatha Tetragnatha Argyrodes Leucauge Misumena nana Total

Thomisidae Runcinia Thomisus spnrifer Zodariidae Tetragnathidae Theridiidae

TABLE 1. Contd. TABLE /speciesFamily 218 N. WOIN et al. TABLE 2. Species richness, abundance and diversity of spiders at Lagbo, Maga and Yagoua, Cameroon

Variable Lagdo Maga Yagoua

2002 2003 2004 2002 2003 2004 2003 2004

Species richness 25 25 27 25 26 27 17 23 Abundance 1,862 2,394 2,229 2,063 2,112 2,220 1,214 2,874 Diversity index (H’) 2.22a 2.06b 2.20b 2.37c 2.19d 2.07e 2.03f 2.06g Evenness (E) 0.69 0.64 0.67 0.74 0.67 0.63 0.72 0.66

Values marked with the same letter across years (rows) within a given site are not significantly different (t-Test, p<0.05)

TABLE 3. Dominance class of spiders (cumulative values) at Lagdo, Maga and Yagoua, Cameroon in 2002 - 2004

Sites Eudominant species (%) Dominant species (%) Sub-dominant species (%)

Lagdo Pardosa spp. (74.12) - Neoscona theisi (7.65) Arctosa spec. ( 6.61) Araneus cereolellus (4.36) Argyrodes spp. (4.15) Allocosa spec. ( 3.11)

Maga Pardosa spp. (44.40) Argyrodes spp. (10.21) Langbiana vokrensis ( 7.74) Arctosa spec. ( 7.33) Cheiracanthium melanostomelum (6.10) Lycosa spp. (5.19) Notioscopus spec. (3.38) Pterartoria spp. (3.62)

Yagoua - Neoscona theisi (16.53) Metaleptyphantes foulfouldei (6.97) Cheiracanthium melanostomelum (13.38) Argyrodes spp. (4.10) Pardosa spp. (20.76) Langbiana vokrensis (27.35)

TABLE 4. Dominance class of ground beetles (cumulative values) at Lagdo, Maga and Yagoua, Cameroon in 2002 - 2004

Sites Eudominant species (%) Dominant species (%)

Lagdo Clivina erythropyga Putzeys (34.4) Abacetus crenulatus Dejean (18.03) Maga Abacetus crenulatus Dejean (55.49) Clivina dumolinii Putzeys (10.7) Yagoua Abacetus foveolatus Chaudoir (50.8) Abacetus crenulatus Dejean (18.0) Biological control of rice yellow mottle virus vectors 219 TABLE 5. Number of ground beetles collected by means of D-Vac at Lagdo, Maga and Yagoua, Cameroon

Family/subfamily/species Lagdo Maga Yagoua

Carabidae

Anchomeninae Metagonum patroboides (Murray) 1 0 3

Graphipterinae Graphipterus obsoletus nigericus Basilewsky 10 21 11

Harpalinae Platymetopus xanthographus (Alluaud) 1 0 0

Masoreinae Aephnidius madagascariensis (Chaudoir) 3 8 5 Masoreus orientalis Dejean 2 0 1

Oodinae Acanthoodes centrosternis (Chaudoir) 3 1 0

Pterostichinae Abacetus crenulatus Dejean 12 118 23 Abacetus foveolatus Chaudoir 2 13 6 Abacetus nitens Tschitscherine (?) 1 4 3

Scaritinae Clivina erythropyga Putzeys 13 14 7 Clivina dumolinii Putzeys 3 19 5 Clivina sp A 2 2 3

Siagoniinae Siagona senegalensis Dejean 3 4 1

Tetragonoderinae Tetragonoderus quadrimaculatus Gory 2 0 6

Zuphiinae Zuphium fuscum Gory 1 0 3

TABLE 6. Dominance class of rove beetles (Cumulative values) at Lagdo, Maga and Yagoua, Cameroon in 2002 - 2004

Species dominance Eudominant species (%) Dominant species (%)

Lagdo Paederus sabaeus Erichson (69.14) Stenus ravus Puthz (17.43) Maga Paederus sabaeus Erichson (84.90) - Yagoua Paederus sabaeus Erichson (53.74) Stenus ravus Puthz (36.30) 220 N. WOIN et al. TABLE 7. Number of rove beetles collected by means D-Vac and Sweep net (2002-2004)

Genera/species Lagdo Maga Yagoua

Paederus alfieri Koch 2 3 1 Paederus sabaeus Erichson 242 391 163 Paederus saengeri Coiffait 2 3 0 Philonthus coprophilus Jarrige 7 0 2 Philonthus turbidus Erichson 0 1 0 Stenus argentatus Puthz 0 1 1 Stenus bauerinae Puthz 3 0 0 Stenus fulgidusPuthz 20 14 9 Stenus furcifer Puthz 0 0 13 Stenus gerardianus Scheerpeltz 1 0 1 Stenus prospector Favel 9 7 0 Stenus ravus Puthz 63 39 92 Stenus tschdensis Puthz 2 1 1

Total 351 460 283

TABLE 8. Hemipteran species with parasitoid status on RYWV insect vectors in Cameroon

Parasitoids Host(s) Stage(s) attacked

Eurytoma spp. Chaetocnema pulla Larva Pediobius spp. Oxya hyla Pupa Pediobius furvus Gahan Trichispa sericae Pupa Chnootriba similis Larva Telenomus sp. Conocephalus longipennis Pupa/larva Tetrastichus spp. Chnootriba similis Larva Locris ruba Pupa/larva

management practices has been shown to result Despite the early emphasis placed on in decreasing importance of Chaetocnema spp. specialist predators and their potential control of in lowland rice (Weber and Parada, 1994). target prey populations, recent evidence indicates Many studies have been conducted on that generalist predators may also have important polyphagous beetles both in natural vegetation influences on prey. They are abundant and various habitats in agro-ecosystems ( Fagel, polyphagous predators in most agricultural 1970 and1973; Puthz, 1971; Thiele, 1977; Luff, systems and are potentially important pest control 1987; Ishitani and Yano, 1994). However, in paddy organisms (Riechert and Lockley, 1984; Nyffeler rice fields, the population dynamics of these and Benz, 1988; Woin, 1999). Spiller’s (1992) insects have not been documented, probably experimental work with two spider species, because of the inundated environment (Yano et demonstrated the potential interference effects al., 1995). In Africa and Latin America where that generalist predators may have on each other’s upland rice represents, respectively, 60 and 73 % predation effects on insect populations. Riechert of total rice-growing area (Jacquot and Courtois, and Bishop (1990), nevertheless, found that in 1993), predatory soil-dwelling beetles may be conserving the spider assemblage by the considered in establishing any integrated insect application of mulch, one can significantly reduce pest management program. phytophagous insect numbers and plant damage. Biological control of rice yellow mottle virus vectors 221 However, little is known about the population Bernhauer, M. 1939. Zur Staphylindenfauna von ecology of Afrotropical species. Among the Kamerun (42. Beitrag). 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